The present invention relates to rotary steerable tools for incorporation into drilling apparatus, and relates particularly, but not exclusively, to such tools for use in the oil and gas well drilling industry.
Rotary steerable tools for incorporation into drilling apparatus for adjusting the direction of drilling of the drilling apparatus are known. Such tools are designed to be incorporated into a drill string and generally comprise a tubular outer housing for engaging the wall of a borehole formed by the drilling apparatus incorporating the tool and a hollow sleeve for transmitting drive from the surface to a drilling bit of the drilling apparatus. The sleeve defines a hollow passage for delivery of drilling fluid to the drill bit. A rotary steerable tool of this type is disclosed in WO 92/09783.
Preferred embodiments of the present invention seek to improve the design of rotary steerable tools.